The present invention relates generally to implantable cardiac stimulation devices, such as pacemakers and implantable cardioverter-defibrillators (ICDs), and, more particularly, to a switch assembly for an implantable cardiac stimulation device which can be selectively configured to electrically connect the case (can) of the device to either a positive or negative polarity high voltage defibrillator output, to thereby electrically "activate" the can so that it can serve as an electrode of the chosen polarity.
Various types of implantable cardiac stimulation devices are presently available for delivering various types of cardiac stimulation therapy. The two most common types which are in widespread use are pacemakers and ICDs. Pacemakers generally produce relatively low voltage pacing pulses which are delivered to the patient's heart through low voltage, "bipolar" pacing leads, generally across spaced-apart ring and tip electrodes thereof which are of opposite polarity. These pacing pulses assist the natural pacing function of the heart in order to prevent bradycardia. Contemporary ICDs are capable of delivering tiered therapy, e.g., bradycardia pacing therapy, antitachycardia pacing therapy, cardioversion therapy, and defibrillation therapy. Each tier or level of therapy requires the delivery of pulses of progressively higher voltage.
Early generation ICDs utilized a lead system which consisted of at least one epicardial patch electrode of a first polarity which was sewn onto the surface of the patient's heart, in combination with another epicardial patch electrode of a second polarity or a transvenous electrode of a second polarity placed in the region of the patient's superior vena cava. A thoracotomy procedure (i.e., a surgical opening of the patient's chest) was required to implant the epicardial patch electrodes.
Fortunately, lead systems have been developed which eliminate the necessity of a thoracotomy. Although there are a variety of different such nonthoracotomy lead systems which are presently known, most contemporary systems utilize a combination of a right ventricular (RV) endocardial lead electrode placed in the apex of the right ventricle of the patient's heart, a superior vena cava (SVC) transvenous lead electrode placed in the region of the SVC of the patient's heart, and, if necessary, a subcutaneous (SubQ) electrode (located underneath the patient's skin in the left chest area). Of course, at least two of these "unipolar" lead electrodes are of opposite polarity. Where two defibrillation electrodes of the same polarity are used, a "Y" adapter may be used to couple both electrodes to a single connector port.
Such nonthoracotomy lead systems can be implanted by the physician at the time that the ICD is implanted, using minimally invasive techniques, e.g., guiding the leads through veins in the upper chest down inside the patient's heart. The SubQ electrode can be a subcutaneous patch electrode, and/or, a conductive portion of the housing or can of the ICD can be used as a SubQ electrode. When the conductive portion of the can is used as an electrode (i.e., electrically connected to a high voltage terminal of the pulse generator circuitry of the ICD), the can is considered "active", and thus, is commonly referred to as an "active can". If not, the can is considered "inactive" or "passive".
Systems that deliver a defibrillation pulse between one or more endocardial electrodes and an active defibrillator housing are disclosed in U.S. Pat. Nos. 4,727,877, issued to Kallok; 4,922,927, issued to Fine et al.; 5,129,394, issued to Mehra; 5,133,353, issued to Hauser; 5,261,400, issued to Bardy; and, 5,374,279, issued to Duffin, Jr. et al., all of which are herein incorporated by reference. As used herein, the terms "housing", "enclosure", "case", and "can" are synonymous.
If the implanting physician chooses to use an active can which is pectorally implanted, it is unlikely that this decision would be changed in the future. If the implanting physician chooses to use a SubQ lead electrode and an inactive can which is abdominally implanted, it is also unlikely that this decision would be later changed. Even if this decision were reversed (i.e., if it were later decided to activate the can), a surgical procedure would likely be required in order to reposition the can for effective use as an electrode. Therefore, external programmability of this choice of active or inactive can is not needed, thereby allowing the design and manufacture of the ICD to be less complex.
In this connection, an ICD which would afford the implanting physician the capability of choosing from a number of different electrode configurations, including can active or inactive, at the time of implant, would be highly beneficial, as such electrode configuration selectability would enable the implanting physician to optimize the defibrillation threshold (DFT), which is the minimum amount of energy required to defibrillate a patient's heart, and thus optimize the defibrillation therapy delivered by the ICD for that patient.
In U.S. Pat. No. 4,301,805, issued to Peers-Trevarton et al., a cardiac pacer connector system is disclosed that is provided with a bridging means for using the pacer case as a reference potential when a unipolar lead is used. When a bipolar pacing/sensing lead is used the bridging means is not operated, and the pacer case is inactive.
In U.S. patent application Ser. No. 08/455,824, filed on May 31,1995 which is a Continuation-In-Part of application Ser. No. 08/221,811, filed Mar. 31, 1994 and abandoned on Oct. 31, 1995, in the name of Pless et al., which is assigned to the assignee of the present in cardiac defibrillator with a case that can be made electrically active or inactive is disclosed. A special connector cavity is provided that has one terminal electrically connected to the pulse generator case and a second terminal connected to one pole of the defibrillator output. By plugging in a pin long enough to contact both terminals, the case is activated during delivery of a defibrillation shock. No means is disclosed therein for using a standard connector pin, such as a DF-1 defibrillator connector pin. The device disclosed in U.S. Pat. No. 5,374, 279, issued to Duffin, Jr. et al., has a similar deficiency in that a special lead connector or plug must be provided to activate the defibrillator case.
Because of the desire to be compatible with existing lead connectors without requiring a special adapter, both at initial implant and during a pulse generator replacement, it would be useful if the pulse generator case could be activated while allowing the use of standard lead connectors.
U.S. patent application Ser. No. 463,527, filed Jun. 5, 1995, in the name of Paspa et al., which is assigned to the assignee of the present invention, the disclosure of which is herein incorporated by reference, discloses a state-of-the-art defibrillator which is provided with a header which includes means for enabling the implanting physician to quickly, safely, and easily select the can to be active (either polarity) or inactive, by merely tightening or not tightening either or both of two setscrews into respective setscrew cavities provided in the header. Similarly, lead connectors (e.g., of RV and SVC lead electrodes) can be selectively inserted or plugged into standard lead connector cavities provided in the header, and setscrews selectively tightened onto the lead connector pins thereof, to thereby selectively activate the inserted lead electrodes. By this simple technique, various electrode configurations can be easily selected to thereby provide the optimum system for a given patient. The defibrillator of this invention is simpler and safer to manufacture and implant than previously known defibrillators, and can be used with previously implanted defibrillation leads. Further, the defibrillator of this invention allows the use of standard lead connectors without requiring a special adapter or a lead having a special connector.
U.S. patent application Ser. No. 353,422, filed Dec. 9, 1994, in the name of Paul Paspa, which is assigned to the assignee of the present invention, the disclosure of which is herein incorporated by reference, discloses another state-of-the-art defibrillator which is provided with a header which includes means for enabling the implanting physician to quickly, safely, and easily select the can to be active or inactive, and/or a lead electrode(s) to be active or inactive, by merely tightening or not tightening either or both of two setscrews into respective setscrew cavities provided in the header. Similarly, lead connectors (e.g., of RV and SVC lead electrodes) can be selectively inserted or plugged into standard lead connector cavities provided in the header, and setscrews selectively tightened onto the lead connector pins thereof, to thereby selectively activate the inserted lead electrodes. By this technique, various electrode configurations can be easily selected to thereby provide the optimum system for a given patient. The defibrillator of this invention is also simpler and safer to manufacture and implant than previously known defibrillators, and can also be used with previously implanted defibrillation leads. Further, the defibrillator of this invention also allows the use of standard lead connectors without requiring a special adapter or a lead having a special connector.
The present invention is directed to an implantable cardiac stimulation device, and a novel switching assembly therefor, which affords the full range of easily selectable electrode configuration options, an which is an alternative to the above-referenced state-of-the-art defibrillators, and which provides certain advantageous features not found in such state-of-the-art defibrillators. These advantageous features, which will become apparent hereinafter, are believed to enhance the manufacturability and reliability of the device.